1. Field of the Invention
The present invention relates to a toner for developing an electrostatic latent image, and image forming method and apparatus using the toner. More particularly, the present invention relates to a toner for use in an image forming method in which a toner image formed on a receiving material is fixed upon application of heat while the toner image is contacting a belt.
2. Discussion of the Background
Currently, image fixing devices using a heat roller are widely used for electrophotographic image forming apparatus such as copiers and printers because the fixing devices have a simple structure and are easy to handle.
However, the image fixing methods using a heat roller have a drawback such that it takes a long time to rise the temperature of the heat roller to a predetermined fixing temperature. In attempting to remedy this drawback, Japanese Laid-Open Patent Publications Nos. 2-160250 and 2-161462 have disclosed image fixing techniques using a combination of a belt fixing device and a toner therefor
In particular, it is desired for electrophotographic color copiers and printers to produce glossy color toner images. Therefore, it is needed to lengthen the fixing time during which a toner image contacts a heat element such as a heat roller (this fixing time is sometimes referred to as a nipping time). In order to lengthen the nipping time, a heat roller having an elastic material thereon is typically used. Elastic materials are generally a heat insulator. Therefore, in color copiers and printers using a heat roller having an elastic material thereon, the waiting time becomes much longer than that in monochrome (black and white) copiers and printers because the elastic material has to be also heated so as to be the predetermined temperature. In image fixing devices using a belt-shaped fixing element (hereinafter referred to as a belt fixing method), a desirable nipping time can be obtained by using a heat insulation belt (i.e., without using an elastic material).
In addition, in color copiers and printers using a heat roller for fixing toner images, it is needed to apply a silicone oil to a pair of fixing rollers (i.e., the heat roller and a pressure roller) in an amount of few milligrams per one copy to securely release toner images from the pair of fixing rollers. When a large amount of a silicone oil is applied thereto, a problem which occurs is that the silicone oil is transferred onto a receiving material. When a transparent sheet for use in overhead projection (OHP) is used as a receiving material, the silicone oil adheres to the transparent sheet, resulting in deterioration of the image qualities of projected color images, such as transparency. In addition, it is unpleasant to touch such oily copy sheets.
In attempting to solve the problems, Japanese Laid-Open Patent Publications Nos. 7-210019 and 8-95287 have disclosed a belt fixing method in which no oil is used (i.e., an oil-less fixing method) or a small amount of an oil is used.
As mentioned above, the belt fixing method has the following advantages:
(1) the wait time is very short;
(2) a small-sized fixing units can be used; and
(3) it is possible to apply no oil or only a small amount of an oil to the belt. However, the belt fixing methods have the following drawbacks:
(1) the life of a belt is short;
(2) image qualities deteriorate when a belt is hurt; In particular, when a color image is fixed using a hurt belt, the resultant fixed color image has an image defect corresponding to the hurt of the belt, such as nonglossy images.
In attempting to prolong the life of a belt, Japanese Laid-Open Patent Publications Nos. 4-328531 and 8-95287 respectively disclose a toner having a specific Wadell sphericity, and a toner including a specific resin which is useful when the toner is manufactured using a pigment master batch. However, their effects are not satisfactory.
Although belt fixing methods have an advantage to shorten the waiting time, the belt fixing methods have a disadvantage such that a plenty of cool receiving materials successively pass through the belt fixing device, the temperature of the belt fixing device varies because the belt fixing device has no heat storage elements. Therefore, problems such that poorly-fixed toner images are produced and/or an offset image problem in which an image is offset to another image tend to occur unless the toner used has a wide fixable temperature range.
Because of these reasons, a need exists for a toner which has a wide fixable temperature range (i.e., which can produce good fixed images even when used for a belt fixing method) and which hardly damage the belt-shaped fixing element.
Accordingly, an object of the present invention is to provide a toner which can produce good fixed images even when used for a toner image fixing method using a belt-shaped fixing element and which hardly damage the belt-shaped fixing element.
Another object of the present invention is to provide a two-component developer which can produce good fixed images even when used for a toner image fixing method using a belt-shaped fixing element and which hardly damage the belt-shaped fixing element.
Yet another object of the present invention is to provide image forming method and apparatus in which the waiting time is short and which can produce good images without image defects for a long time.
A further object of the present invention is to provide a method for manufacturing the toner mentioned above.
Briefly these objects and other objects of the present invention as hereinafter will become more readily apparent can be attained by a toner including a colorant which is dispersed in the toner and which has an average major particle diameter not greater than 0.5 xcexcm, wherein the toner has the following property:
Taxe2x89xa6100 (xc2x0 C.), and (Tbxe2x88x92Ta)xe2x89xa77.0 (xc2x0 C.)
wherein Ta represents a temperature at which the toner has a melt viscosity of 50,000 Paxc2x7sec and Tb represents a temperature at which the toner has a melt viscosity of 5,000 Paxc2x7sec.
Preferably, the toner is provided using a process of preparing a pigment master batch in which toner constituents including at least a colorant and a resin are kneaded while being heated at a temperature ranging from a glass transition temperature of the resin to a temperature higher than the glass transition temperature by 40xc2x0 C.
In another aspect of the present invention, an image forming method is provided which includes the steps of:
providing the toner mentioned above;
developing an electrostatic latent image with the toner to prepare a toner image;
transferring the toner image on a receiving material; and
bringing the toner image on the receiving material into contact with a belt or an endless belt of a belt fixing device to fix the toner image.
It is possible to prepare a color image by performing the developing steps in plural times using plural color toners, for example, a cyan, magenta and yellow color toner.
In further aspects of the present invention, a toner container including the toner mentioned above and an image forming apparatus having the toner container are provided.
In a still further aspect of the present invention, a two-component developer is provided which includes a carrier and the toner mentioned above. The carrier is preferably one from which carrier particles having a relatively low magnetic force are previously removed.
In still further aspects of the present invention, a developer container including the developer mentioned above and an image forming apparatus having the developer container are also provided.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.